1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a reflective liquid crystal display device and a fabricating method thereof. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for improving a contrast ratio of a liquid crystal display device.
2. Discussion of the Related Art
Generally, liquid crystal display (LCD) devices are classified into two types depending upon the usage of a light source: a transmissive LCD device using a backlight and a reflective LCD device using an external natural and/or artificial light source. More than about two thirds of a total power are consumed for the backlight in the transmissive LCD device, whereas the power consumption is improved in the reflective LCD devices due to the absence of the backlight.
In the reflective LCD device, a black matrix is used to improve a contrast ratio. However, a contrast ratio is reduced as a black matrix reduces a reflective portion.
FIG. 1 is an expanded perspective view of a reflective liquid crystal display device according to a related art. In FIG. 1, first and second substrates 6 and 23 face into and are spaced apart from each other. A data line 17 and a gate line 5 are formed on the inner surface of the first substrate 6. Each of the data line 17 and the gate line 5 crosses each other and defines a pixel region “P”. A thin film transistor (TFT) “T” is formed at each intersection between the data line 17 and the gate line 5. A pixel electrode (i.e., a reflective electrode 18) is formed at the pixel region “P”. The reflective electrode 18 is formed of a conductive material such as aluminum (Al) having an excellent conductivity and reflectance, and an Al alloy. A black matrix 21 is formed on the inner surface of the second substrate 23 in a matrix form. A color filter layer 22 including sub-color filters 22a, 22b, and 22c is formed at an inner portion of the matrix corresponding to the pixel region “P”. A transparent common electrode 24 is formed on the entire surface of the second substrate 23. A liquid crystal layer 20 is interposed between the first and second substrates 6 and 23.
The black matrix 21 is formed at regions corresponding to the data line 17, the gate line 5, and the thin film transistor “T”. The black matrix 21 is designed in consideration of a misaligned margin during the attachment process of the first and second substrates 6 and 23. Accordingly, the area of the black matrix 21 is increased.
FIG. 2 is a schematic cross-sectional view taken along line II-II of FIG. 1. FIG. 3 is a magnified cross-sectional view of a portion “A” of FIG. 2.
As shown in FIGS. 2 and 3, a data line 17 is formed between adjacent pixel regions “P1” and “P2” on the inner surface of a first substrate 6. A black matrix 21 corresponding to the data line 17 and a color filter layer 22 including sub-color filters 22a, 22b, and 22c corresponding to the pixel regions “P1” and “P2” are formed on the inner surface of a second substrate 23. When a first distance between adjacent reflective electrodes 18 over the data line 17 is “a” and a second distance of the portion of the reflective electrodes 18 overlapping the data line 17 is “b”, a width of the black matrix 21 becomes “a+2b”. Since a uniform electric field is not sufficiently applied to a liquid crystal layer (not shown) corresponding to the first distance “a” unlike on the reflective electrode 18, light is leaked through the liquid crystal layer corresponding to the first distance “a” even when a voltage corresponding to a black state of the pixel region “P” is applied in a normally white mode. Therefore, the black matrix 21 should shield the region corresponding to the first distance “a”. Furthermore, a value of “2b” corresponds to a misaligned margin during the attachment process of the first and second substrates 6 and 23. Therefore, the area of the black matrix 21 is increased, thereby decreasing an effective reflection area, which is not suitable for a reflective liquid crystal display device requiring high luminance.
In the reflective LCD device, as mentioned above, it is important to improve brightness and a contrast ratio because the ambient light reflected at the reflective electrode is used instead of the backlight to display images. The black matrix improving a contrast ratio may prevent the light leakage in the region corresponding to the data line. However, an overlapping region of the black matrix and the data line reduces an effective reflection area, thereby reducing the brightness.